C++ cmpxchg函数代码示例

void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
{
	struct fscrypt_info *prev;

	if (ci == NULL)
		ci = ACCESS_ONCE(inode->i_crypt_info);
	if (ci == NULL)
		return;

	prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
	if (prev != ci)
		return;

	put_crypt_info(ci);
}

void f2fs_free_encryption_info(struct inode *inode, struct f2fs_crypt_info *ci)
{
	struct f2fs_inode_info *fi = F2FS_I(inode);
	struct f2fs_crypt_info *prev;

	if (ci == NULL)
		ci = ACCESS_ONCE(fi->i_crypt_info);
	if (ci == NULL)
		return;
	prev = cmpxchg(&fi->i_crypt_info, ci, NULL);
	if (prev != ci)
		return;

	f2fs_free_crypt_info(ci);
}

int page_nid_xchg_last(struct page *page, int nid)
{
	unsigned long old_flags, flags;
	int last_nid;

	do {
		old_flags = flags = page->flags;
		last_nid = page_nid_last(page);

		flags &= ~(LAST_NID_MASK << LAST_NID_PGSHIFT);
		flags |= (nid & LAST_NID_MASK) << LAST_NID_PGSHIFT;
	} while (unlikely(cmpxchg(&page->flags, old_flags, flags) != old_flags));

	return last_nid;
}

static void net_secret_init(void)
{
	u32 tmp;
	int i;

	if (likely(net_secret[0]))
		return;

	for (i = NET_SECRET_SIZE; i > 0;) {
		do {
			get_random_bytes(&tmp, sizeof(tmp));
		} while (!tmp);
		cmpxchg(&net_secret[--i], 0, tmp);
	}
}

/*
 * FIXME: this is hack to save delta to linux buffer_head.
 * Inefficient, and this is not atomic with dirty bit change. And this
 * may not work on all arch (If set_bit() and cmpxchg() is not
 * exclusive, this has race).
 */
static void tux3_set_bufdelta(struct buffer_head *buffer, int delta)
{
	unsigned long state, old_state;

	delta = tux3_delta(delta);

	state = buffer->b_state;
	for (;;) {
		old_state = state;
		state = tux3_bufsta_update(old_state, delta);
		state = cmpxchg(&buffer->b_state, old_state, state);
		if (state == old_state)
			break;
	}
}

void mce_log(struct mce *mce)
{
	unsigned next, entry;
	int ret = 0;

	/* Emit the trace record: */
	trace_mce_record(mce);

	ret = atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, mce);
	if (ret == NOTIFY_STOP)
		return;

	mce->finished = 0;
	wmb();
	for (;;) {
		entry = rcu_dereference_check_mce(mcelog.next);
		for (;;) {

			/*
			 * When the buffer fills up discard new entries.
			 * Assume that the earlier errors are the more
			 * interesting ones:
			 */
			if (entry >= MCE_LOG_LEN) {
				set_bit(MCE_OVERFLOW,
					(unsigned long *)&mcelog.flags);
				return;
			}
			/* Old left over entry. Skip: */
			if (mcelog.entry[entry].finished) {
				entry++;
				continue;
			}
			break;
		}
		smp_rmb();
		next = entry + 1;
		if (cmpxchg(&mcelog.next, entry, next) == entry)
			break;
	}
	memcpy(mcelog.entry + entry, mce, sizeof(struct mce));
	wmb();
	mcelog.entry[entry].finished = 1;
	wmb();

	mce->finished = 1;
	set_bit(0, &mce_need_notify);
}

void ext4_free_encryption_info(struct inode *inode,
			       struct ext4_crypt_info *ci)
{
	struct ext4_inode_info *ei = EXT4_I(inode);
	struct ext4_crypt_info *prev;

	if (ci == NULL)
		ci = ACCESS_ONCE(ei->i_crypt_info);
	if (ci == NULL)
		return;
	prev = cmpxchg(&ei->i_crypt_info, ci, NULL);
	if (prev != ci)
		return;

	ext4_free_crypt_info(ci);
}

static void check_lock(struct lock_debug *debug)
{
    int irq_safe = !local_irq_is_enabled();

    if ( unlikely(atomic_read(&spin_debug) <= 0) )
        return;

    /* A few places take liberties with this. */
    /* BUG_ON(in_irq() && !irq_safe); */

    if ( unlikely(debug->irq_safe != irq_safe) )
    {
        int seen = cmpxchg(&debug->irq_safe, -1, irq_safe);
        BUG_ON(seen == !irq_safe);
    }
}

int bbgl_mutex_lock(bbgl_mutex_t *mutex) {
    int c;
    for (int i = 0; i < 100; i++) {
        c = cmpxchg(mutex, 0, 1);
        if (c == 0)
            return 0;
        __asm__ __volatile__("pause" ::: "memory");
    }
    if (c == 1)
        c = xchg(mutex, 2);
    while (c) {
        futex(mutex, FUTEX_WAIT, 2, NULL, NULL, 0);
        c = xchg(mutex, 2);
    }
    return 0;
}

static void j2_send_ipi(unsigned int cpu, unsigned int message)
{
	volatile unsigned *pmsg;
	unsigned old;
	unsigned long val;

	/* There is only one IPI interrupt shared by all messages, so
	 * we keep a separate interrupt flag per message type in sw. */
	pmsg = &per_cpu(j2_ipi_messages, cpu);
	do old = *pmsg;
	while (cmpxchg(pmsg, old, old|(1U<<message)) != old);

	/* Generate the actual interrupt by writing to CCRn bit 28. */
	val = __raw_readl(j2_ipi_trigger + cpu);
	__raw_writel(val | (1U<<28), j2_ipi_trigger + cpu);
}

int gre_del_protocol(const struct gre_protocol *proto, u8 version)
{
	int ret;

	if (version >= GREPROTO_MAX)
		return -EINVAL;

	ret = (cmpxchg((const struct gre_protocol **)&gre_proto[version], proto, NULL) == proto) ?
		0 : -EBUSY;

	if (ret)
		return ret;

	synchronize_rcu();
	return 0;
}

/*
 * Claim the entry so that no one else will poke at it.
 */
static bool irq_work_claim(struct irq_work *work)
{
	unsigned long flags, nflags;

	for (;;) {
		flags = work->flags;
		if (flags & IRQ_WORK_PENDING)
			return false;
		nflags = flags | IRQ_WORK_FLAGS;
		if (cmpxchg(&work->flags, flags, nflags) == flags)
			break;
		cpu_relax();
	}

	return true;
}

unsigned long long
uisqueue_interlocked_and(unsigned long long __iomem *tgt,
			unsigned long long set)
{
	unsigned long long i;
	unsigned long long j;

	j = readq(tgt);
	do {
		i = j;
		j = cmpxchg((__force unsigned long long *)tgt, i, i & set);

	} while (i != j);

	return j;
}

int ip_tunnel_encap_del_ops(const struct ip_tunnel_encap_ops *ops,
			    unsigned int num)
{
	int ret;

	if (num >= MAX_IPTUN_ENCAP_OPS)
		return -ERANGE;

	ret = (cmpxchg((const struct ip_tunnel_encap_ops **)
		       &iptun_encaps[num],
		       ops, NULL) == ops) ? 0 : -1;

	synchronize_net();

	return ret;
}

static u16 nvmet_install_queue(struct nvmet_ctrl *ctrl, struct nvmet_req *req)
{
	struct nvmf_connect_command *c = &req->cmd->connect;
	u16 qid = le16_to_cpu(c->qid);
	u16 sqsize = le16_to_cpu(c->sqsize);
	struct nvmet_ctrl *old;

	old = cmpxchg(&req->sq->ctrl, NULL, ctrl);
	if (old) {
		pr_warn("queue already connected!\n");
		return NVME_SC_CONNECT_CTRL_BUSY | NVME_SC_DNR;
	}

	nvmet_cq_setup(ctrl, req->cq, qid, sqsize);
	nvmet_sq_setup(ctrl, req->sq, qid, sqsize);
	return 0;
}